Radar display



June 10, 1952 E. G. SCHNEIDER RADAR DISPLAY 2 SHEETS- SHEET 1 Original Filed Feb. 3, 1945 INVENTOR.

I EDW|N G. SCHNEIDER BY w MM5 Amr/79j June 10, 1952 E. G. SCHNEIDER E 2,600,335

RADAR DISPLAY Original Filed Feb. 3, 1945 2 SHEETS- SHEET 2 FIG. 2

V A JNVENToR.

EDWIN G. SCHNEIDER ATTORNEY Patented June 10, 1952 UNITE SATS by mesne assignments, to the United States of America as represented by theSecretary of War Grginal application February 3, 1.945', Serial No. 576,115, now Patent No. 2,555,163,- datedMay 29, 1951. Divided and this' application July 22, 1948, Serial No. 40,143

4 Claims. 1

This invention relates generally to control of the display by varying the time of initiating the sweep of the electron beam of a cathode ray indicator tube utilized in radio object locating equipment to display azimuth and range information.

rhis application is a division of my application Serial Number 576,115, led. February 3, 1945, now Patent Number 2,555,163, dated May 29, 1951-.

Certain types of radio object locating equipment are provided with a cathoderay tube indicator having a radial sweep reaching from the center of the screen to the periphery and rotated about the tube axis. The reected echoes control the electron beam intensity so that reflecting objects produce an indication on the screen having an angular position corresponding to the azimuth of the detected object, and having a, distance from the center of the screen corresponding to the range of the object. This type of display is known as plan position ind-ication (P. P. Il)

Olne of the objects of this invention is to expand the indicator sweep so that a `selected portion of the range is spread over the enti-re indicator screen.

This system has been tested and found highly successful in radio object locating equipment SCR 615A, andl has been adapted to various other equipment of similar nature.

Other objects` will be apparent from a study of the following specification, taken in connection with the accompanying drawing, in which:

Fig. 1 is a block diagram of a radio object loeating apparatus utilizing a P. P. I. display and assembled in accordance with the principles of this invention; and

Fig. 2' shows the approximate wave shapes of the output of the major components of said system.

Referring now more particularly to Fig. 1 of the drawing, a master oscillator I is provided having a sine wave output of a frequency depending upon the maximum eiiective range of the system. Assuming that said maximum range is 100 miles, a pulse frequency or' repetition rate of 930 C; P. S. is suitable to allow a radio pulse to reach a target at the maximum eiective range and permit any' echo thereof to be receivedV back by the equipment before the transmission of the next-radio pulse.

The sine wave output of oscillator I0 is distorted in a keyer II to obtain narrow flat top pulses. The pulse output of keyer II is" applied i'n part to a radio frequency oscillator or transmitter I2 whereby short pulses of radio frequency energy are obtained which, through a duplexing circuit I3 may be conveyed to a highly directional antenna system I5 adapted to be rotated, preferably continuously through 360 o'f azimuth. Duplexing circuit I3 is a switch for connecting transmitter I'2 to antenna I5 during the trans# mission of pulses and for connecting receiver I4 to antenna I5 during alternate periods in order to protect receiver I4 from undue shock during transmission periods. The antenna system I5 may comprise suitable dipole radiating elements and an appropriate parabolic reflector, designed to concentrate the transmitted energyinto a re1- ativ'ely narrow beam.

The output of the keyer Il is also utilized to control the operation of a suitable circuit I6 adapted to generate sharp triggering pulses which, through a manually operated switching arrangement Il, may be applied to a sweep' generator I8'. The output of the latter, a sawtooth current, is applied to deflecting coils I9 rotatable about the neck of a cathode ray tube 20 at a rate corresponding to that of the rotation of the antenna system I5. By this arrangement the screen of the indicator tube' 20 is provided with a radial electron beam trace commencing at its center" and extending to its periphery.

The above described trace is' rotated' about its origin in synchronism with the azimuthal scanning of the antenna system I5. The radial' trace and antenna system are both initially aligned with zero degrees azimuth', corresponding to transmission in a reference direction, for example, north. IIn the example being described the trace represents v miles, and therefore the generato'r I`8 should be designed so that the'ti'me base output thereof is equal to 1075 microseconds.v

When transmitted radio pulses encounter a reflecting object, echoes are received by'th'e` antenna system I5 and' conveyed through' the' duplex'i'ng circuit I3 to the receiver I4, where they are demod'ulated and then applied toi the control grid' 2| of the indicator 20. Thus', the electron beam emanating from the cathode 22' ofthe tube 2D becomes intensity-modulated and'there appear on the sensitized screen 23 of said tube, short arcs whose positions depend', as hereinbefore stated, upon the respective azimuths and ranges of the reflecting objects. The' indicator screen may be calibrated about its.V periphery', as at 24, in terms of azimuth; and along a reference diameter, as at 25, in terms of range.

In Fig; 1' of the drawings, two targety indications are shown onl the right-"hand sd'e'" of the shapes shown in Fig. 2 of the drawing as well as to the block diagram of Fig. 1.

At A in Fig. 2, there is diagrammatically represented the pulse output of the sweep trigger generator I6. As above stated, this output is fed to the switch |1, in one of the positions of which, here shown as the upper, said output is applied to the search sweep generator I8. In the other position of said switch, the trigger pulse output of the generator I6 is applied to a conventional buffer amplier 25, where it is inverted, as shown in Fig. 2B.

The positive-going pulses thus obtained which, it will be recalled, are synchronized with the radio pulse transmission, are applied in part to any preferred, highly accurate rectangular wave generator 21 for producing positive-going rectangular waves of selectively variable width, as shown in Fig. 2C. Such rectangular wave generators are well known in the art, an example thereof being shown on page 176 and Figs. 4-9 in Ultra High Frequency Techniques by Brainerd, Koehler, Reich, and Woodruff, published by D. Van Nostrand Co., Inc., in 1942. Generator 21 may be provided with a selector switch 39 for adjusting the length of the rectangular wave produced. y

The adjustable lagging edge of the rectangular wave produced by generator 21 is then dinerentiated in a circuit `28 having a short time constant, to obtain the sharp triggering pulses shown at D in Fig. 2, said pulses then being inverted by a conventional inverter amplier 29 to obtain the positive-going pulses shown at E in Fig. 2. These pulses are utilized to trigger a gate generator 30 producing a positive-going rectangular output wave. Generator 30 may be similar to generator 21, except that it produces rectangular waves of fixed width. In the case under consideration, the waves may have a width of approximately 107.5 microseconds, which is the time required for the radio pulses to travel out and be reflected back over 10 miles, the distance to be represented by the expanded sweep referred to in the earlier portions of this specication.

The resulting rectangular enabling wave or gate, diagrammatically shown in Fig. 2F, is adjustable in phase or time relation with respect to the radio pulse transmission and is applied to one of the control'elements of a normally inoperative standard coincidence circuit 3| to condition said circuit for operation at any time within the period of said gate. Such coincidence circuits are well Iknown in the art and may comprise an electron tube operated with a bias rendering it inoperative unless it is supplied with two pulses, additively and simultaneously, one pulse alone not being sufficient to render the tube operative. Each of the two pulses may be applied to a different electrode of the electron tube.

It will be noted from the description thus far that, by adjusting the width of the output wave (Fig. 2C) of the rectangular wave generator 21, by means of selector switch 39, the application of the gate (Fig. 2F) to the coincidence circuit 3| may be delayed by any desired interval which, for example, may be the sum of increments of time representing 10 miles of range.

I shall now set forth the manner in which the coincidence circuit 3|, after conditioning as just described, is rendered operative to enable triggering of the expanded sweep.

For this purpose, the output of the buffer amplier 26 in addition to being applied to the rectangular wave generator 21, is also applied to an oscillator gate generator 32, which is similar to generator 21 and has a positive-going rectangular output wave of adjustable width as shown at G in Fig. 2. This output is applied to a conventional normally inoperative stable oscillator 33, which, for the duration of said rectangular output wave, generates a sine wave, shown in Fig. 2H, the frequency of which is a submultiple of the frequency or pulse repetition rate of the transmitted radiant energy. In the embodiment described, the frequency of oscillator 33 is 9300 C. P. S., corresponding to a period of 107.5 microseconds.

The positive alternations of said sine waves are distorted by a squarer-amplier 34 to obtain the square-wave train shown in Fig. 21. Squaring circuits are well known in the art and may consist of a top-clipper tube followed by an amplication stage.

The wave shown in Fig. 21 is differentiated in a circuit 35, Fig. 1, as shown in Fig. 2J, and is then clipped and inverted in an appropriate circuit 36, to obtain the trigger pulses shown diagrammatically in 2K. These pulses are separated by the exact time required for the radio pulses to travel out and be reflected back over 10 miles, the distance to be represented by the expanded sweep trace.

The pulse output of the clipper-inverter 3B is applied to the second control element of the coincidence circuit 3|, and whichever pulse occurs during the period when said coincidence circuit is conditioned for operation as above described by the gate shown in Fig. 2F, causes said circuit to pass said pulse, as shown in Fig. 2L. The latter pulse triggers an expanded sweep generator 31, Fig. 1, adapted to produce a sawtooth current whose period is, in the case being considered, 107.5 micro-seconds, representing a range of 10 miles. The output of the expanded sweep generator has a. wave form similar to that of the search sweep generator applied to the deflecting coils |9 of the cathode-ray indicator tube 20.

The range scale on screen 23 of indicator tube 20 relating to the expanded sweep, which is shown on the left-hand side of the screen 23, may be calibrated in terms of range, as shown at 38.

Assuming that the delay introduced by the square wave generator 21 is 322.5 microseconds, which is the time required for the radio pulses to travel out and be reflected back over 30 miles, the commencement of the expanded sweep will have been delayed by that amount of time, so that the trace appearing upon the indicator screen will represent the 10-mile region of space between 30 and 40 miles from the radio-echo equiment. And, it will be noted that the expanded sweep now enables an accurate determination of the ranges of the detected targets. Inspection of the display indicates that the two targets hereinbefore referred to, which were known to be merely somewhere between 30 and 40 miles distant, are actually 34.5 and 37.5 miles distant, respectively.

The foregoing is a description of a preferred embodiment of my present invention, and it will be noted from all of the foregoing that I have provided a simple circuit arrangement for examining closely any selected region of the total range of a P. P. I. object locating system, particularly an early Warning system, whereby the ranges of distant targets detected during normal searching may be determined with greater accuracy than has heretofore been possible.

Other advantages of my present invention Will readily occur to those skilled in the art to which the same relates.

What is claimed is:

1. A pulse echo object locating system comprising means to radiate pulses into space, means to receive echoes of said pulses reilected by objects to be detected, at least one of said means having a directive characteristic, means to vary said directive characteristic for each successive pulse, means to generate time loci on a modified polar coordinate display corresponding in direction to said directive characteristic, means responsive to said receiving means for causing visible indications on said display along said loci upon receipt of an echo, means to synchronize said radiated pulses in predetermined time relation to the generation of said time loci including means to delay the initiation of the generation of said time loci by a predetermined variable time after radiation of each pulse, whereby a positional presentation of the reflecting objects is formed on said display, omitting objects within the distance corresponding to said time to provide a detailed presentation of objects beyond said distance.

2. A pulse echo object locating system comprising means to radiate pulses into space, means to receive echoes of said pulses reflected by objects to be detected, at least one of said means having a directive characteristic, means to vary said directive characteristic for each successive pulse.

means to generate time loci from a point of origin on a modified polar coordinate display in a direction corresponding to said directive characteristic, said receiving means causing visible indication on said display along said loci upon receipt of an echo, means to synchronize said radiated pulses in predetermined time relation to the generation of said time loci including means to delay the initiation of the generation of said time loci by a predetermined variable time after radiation of each pulse, whereby a map-like presentation of the reflecting objects on said display is distorted to omit objects within the distance corresponding to said time and to provide a detailed presentation of objects beyond said distance.

3. A pulse echo object locating system according to claim 1, wherein said time loci are radial sweep traces.

4. A pulse echo object locating system according to claim 2, wherein said time loci are radial sweep traces.

EDWIN G. SCHNEIDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,395,966 Goldberg Mar. 5, 1946 2,422,204 Meacham June 17, 1947 2,426,217 I-Ioisington Aug. 26, 1947 2,426,989 De Rosa Sept. 9, 1947 2,453,711 Isbister et al Nov. 16, 1948 2,454,782 De Rosa Nov. 30, 1948 2,461,998 Patterson Feb. 15, 1949 2,468,032 Busignies Apr. 26, 1949 2,471,516 Bryant May 31, 1949 

